avoid exposing stack overflow bug in unify/unify: use unify/get-in, not get-in, to be sure to deref all references
small optimization: if head is nil, don't call (moreover-head) on it.
increase logging and debugging to catch stack overflow and top-level head filtering not working.
use lexiconf/fn and unify/get-in.
(first (take 1)), not just (take 1)
add sentential adverb :pred values
less logging